Light emitting device and display apparatus including the same

ABSTRACT

Provide is a light emitting device including a reflective layer including a phase modulation surface, a planarization layer disposed on the reflective layer, a first electrode disposed on the planarization layer, an organic emission layer disposed on the first electrode and configured to emit visible light that includes light of a first wavelength and light of a second wavelength that is shorter than the first wavelength, and a second electrode disposed on the organic emission layer, wherein the reflective layer and the second electrode form a micro cavity configured to resonate the light of the first wavelength, and wherein the planarization layer includes a light absorber configured to absorb the light of the second wavelength.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 17/112,363, filed Dec. 4, 2020, which claims priority to KoreanPatent Application No. 10-2020-0026796, filed on Mar. 3, 2020, in theKorean Intellectual Property Office, the disclosure of which isincorporated herein in its entirety by reference.

BACKGROUND 1. Field

Example embodiments of the present disclosure relate to a light emittingdevice and a display apparatus including the light emitting device, andmore particularly to, an organic light emitting device having high colorpurity without using a color filter and an organic light emittingdisplay apparatus.

2. Description of Related Art

An organic light emitting device (OLED) is a display apparatus thatforms an image via light emission according to a combination of holessupplied from an anode and electrons supplied from a cathode in anorganic emission layer. The OLED has excellent display characteristicssuch as a wide viewing angle, a fast response speed, a thin thickness, alow manufacturing cost, and a high contrast.

Further, the OLED may emit a desired color according to selection of anappropriate material as a material of the organic emission layer.According to this principle, it may be possible to manufacture a colordisplay apparatus by using the OLED. For example, an organic emissionlayer of a blue pixel may include an organic material that generatesblue light, an organic emission layer of a green pixel may include anorganic material that generates green light, and an organic emissionlayer of a red pixel may include an organic material that generates redlight. Also, a white OLED may be manufactured by arranging a pluralityof organic materials which respectively generate blue light, greenlight, and red light in one organic emission layer or by arranging pairsof two or more types of organic materials in a complementaryrelationship with each other.

SUMMARY

One or more example embodiments provide a light emitting device and adisplay apparatus having high color purity without using a color filterby using a planarization layer including a micro cavity having a phasemodulation surface and a light absorber.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the example embodiments of the disclosure.

According to an aspect of an example embodiment, there is provide alight emitting device including a reflective layer including a phasemodulation surface, a planarization layer disposed on the reflectivelayer, a first electrode disposed on the planarization layer, an organicemission layer disposed on the first electrode and configured to emitvisible light that includes light of a first wavelength and light of asecond wavelength that is shorter than the first wavelength, and asecond electrode disposed on the organic emission layer, wherein thereflective layer and the second electrode form a micro cavity configuredto resonate the light of the first wavelength, and wherein theplanarization layer includes a light absorber configured to absorb thelight of the second wavelength.

The phase modulating surface of the reflective layer may include aplurality of protrusions that are periodically two-dimensionally formed,and a resonance wavelength of the micro cavity may be determined basedon a width or a diameter of each of the plurality of protrusions, aheight of each of the plurality of protrusions, and distances betweenthe plurality of protrusions.

When the first wavelength is A, the width or the diameter of each of theplurality of protrusions, the height of each of the plurality ofprotrusions, and the distances between the plurality of protrusions maybe set such that an optical length of the micro cavity is equal to nλ/2,where n is a natural number.

The phase modulating surface of the reflective layer may further includea plurality of recesses that are periodically two-dimensionally formed.

The plurality of recesses may be configured to absorb the light of thesecond wavelength.

The plurality of protrusions and the plurality of recesses may contactthe planarization layer.

Each of the plurality of protrusions and each of the plurality ofrecesses may have a cylindrical shape or a polygonal column shape.

A dimension of each of the plurality of protrusions and a dimension ofeach of the plurality of recesses may be less than a wavelength of thevisible light.

A diameter of each of the plurality of recesses may be less than orequal to 250 nm.

A difference between a diameter of each of the plurality of protrusionsand the diameter of each of the plurality of recesses may be less thanor equal to 100 nm.

A height of each of the plurality of protrusions and a depth of each ofthe plurality of recesses may be less than or equal to 100 nm.

The first electrode may be a transparent electrode, and the secondelectrode may be a semi-transmissive electrode configured to reflect aportion of light and transmit a remaining portion of the light.

The second electrode may include a reflective metal, and a thickness ofthe second electrode may be 10 nm to 20 nm.

The planarization layer may include a material that is transparent tothe visible light, and a plurality of light absorbers may be dispersedin the planarization layer.

The visible light may be white light, the light of the first wavelengthmay include red light or green light, and the light of the secondwavelength may include blue light.

The organic emission layer may include a hole injection layer disposedon the first electrode, an organic emission material layer disposed onthe hole injection layer, and an electron injection layer disposed onthe organic emission material layer.

According to another aspect of an example embodiment, there is provide adisplay apparatus including a first pixel configured to emit light of afirst wavelength, and a second pixel configured to emit light of asecond wavelength different from the first wavelength, the first pixelincluding a reflective layer including a phase modulation surface, aplanarization layer disposed on the reflective layer, a first electrodedisposed on the planarization layer, an organic emission layer disposedon the first electrode and configured to emit visible light thatincludes the light of the first wavelength and the light of the secondwavelength that is shorter than the first wavelength, and a secondelectrode disposed on the organic emission layer, wherein the reflectivelayer and the second electrode form a micro cavity configured toresonate the light of the first wavelength, and wherein theplanarization layer includes a light absorber configured to absorb thelight of the second wavelength.

The phase modulating surface of the reflective layer may include aplurality of protrusions that are periodically two-dimensionally formed,and a resonance wavelength of the micro cavity may be determined by awidth or a diameter of each of the plurality of protrusions, a height ofeach of the plurality of protrusions, and distances between theplurality of protrusions.

When the first wavelength is A, a width or a diameter of each of theplurality of protrusions, a height of each of the plurality ofprotrusions, and distances between the plurality of protrusions may beset such that an optical length of the micro cavity is equal to nλ/2,where n is a natural number.

The phase modulating surface of the reflective layer may further includea plurality of recesses that are periodically two-dimensionally formed.

The plurality of recesses may be configured to absorb the light of thesecond wavelength.

The plurality of protrusions and the plurality of recesses may contactthe planarization layer.

A dimension of each of the plurality of protrusions and a dimension ofeach of the plurality of recesses may be less than a wavelength of thevisible light.

The second pixel may include a reflective layer including a flatsurface, a planarization layer disposed on the reflective layer of thesecond pixel, a first electrode disposed on the planarization layer ofthe second pixel, an organic emission layer disposed on the firstelectrode of the second pixel and configured to emit the visible lightthat includes the light of the first wavelength and the light of thesecond wavelength, and a second electrode disposed on the organicemission layer of the second pixel, wherein the reflective layer of thesecond pixel and the second electrode of the second pixel form a microcavity configured to resonate the light of the second wavelength.

The planarization layer of the second pixel may not include the lightabsorber configured to absorb the light of the second wavelength.

The planarization layer of the second pixel may include the lightabsorber configured to absorb the light of the second wavelength.

The reflective layer of the first pixel and the reflective layer of thesecond pixel may extend continuously.

The planarization layer of the first pixel and the planarization layerof the second pixel may extend continuously.

A physical thickness of the first pixel and a physical thickness of thesecond pixel may be same.

The visible light may be white light, the light of the first wavelengthmay include red light or green light, and the light of the secondwavelength may include blue light.

The display apparatus may further include a third pixel configured toemit light of a third wavelength different from the first wavelength andthe second wavelength, respectively, the third pixel may include areflective layer including a phase modulation surface, a planarizationlayer disposed on the reflective layer of the third pixel, a firstelectrode disposed on the planarization layer of the third pixel, anorganic emission layer disposed on the first electrode of the thirdpixel and configured to emit the visible light that includes the lightof the first wavelength, the light of the second wavelength, and thelight of the third wavelength, and a second electrode disposed on theorganic emission layer of the third pixel, wherein the reflective layerof the third pixel and the second electrode of the third pixel form amicro cavity configured to resonate the light of the third wavelength.

The planarization layer of the third pixel may include the lightabsorber configured to absorb the light of the second wavelength that isshorter than the third wavelength.

The light absorber of the first pixel and the light absorber of thethird pixel may include different materials.

A physical thickness of the first pixel, a physical thickness of thesecond pixel, and a physical thickness of the third pixel may be same.

The visible light may be white light, the light of the first wavelengthmay include red light, the light of the second wavelength may includeblue light, and the light of the third wavelength may include greenlight.

According to an aspect of an example embodiment, there is provide alight emitting device including a reflective layer including a phasemodulation surface, the phase modulation surface including a pluralityof protrusions and a plurality of recesses, a planarization layerdisposed on the reflective layer, a first electrode disposed on theplanarization layer, an organic emission layer disposed on the firstelectrode and configured to emit visible light that includes light of afirst wavelength and light of a second wavelength that is shorter thanthe first wavelength, and a second electrode disposed on the organicemission layer, wherein the reflective layer and the second electrodeform a micro cavity configured to resonate the light of the firstwavelength, and wherein the planarization layer includes a lightabsorber configured to absorb the light of the second wavelength.

A resonance wavelength of the micro cavity may be determined based on awidth or a diameter of each of the plurality of protrusions, a height ofeach of the plurality of protrusions, and distances between theplurality of protrusions, and the plurality of recesses may beconfigured to absorb the light of the second wavelength

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects, features, and advantages of exampleembodiments of the disclosure will be more apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a cross-sectional view schematically showing a structure of alight emitting device according to an example embodiment;

FIG. 2 is a cross-sectional view showing in more detail an examplestructure of an organic emission layer illustrated in FIG. 1 ;

FIG. 3 is a cross-sectional view showing in more detail another examplestructure of an organic emission layer illustrated in FIG. 1 ;

FIG. 4 is a perspective view schematically showing an example structureof a reflective layer illustrated in FIG. 1 ;

FIG. 5 is a perspective view schematically showing another examplestructure of a reflective layer illustrated in FIG. 1 ;

FIG. 6 is a graph showing an example of the absorption characteristicsof a planarization layer including a light absorber;

FIG. 7 is a cross-sectional view showing a structure of a light emittingdevice according to a first related example;

FIG. 8 is a cross-sectional view showing a structure of a light emittingdevice according to a second related example;

FIG. 9 is a cross-sectional view showing a structure of a light emittingdevice according to a third related example;

FIG. 10 is a graph showing comparisons of spectrums of light emittedfrom the light emitting devices according to the first to third relatedexamples and the example embodiment;

FIG. 11 shows comparisons of color coordinates of the light emitted fromthe light emitting devices according to the first to third relatedexamples and the example embodiment;

FIG. 12 is a cross-sectional view schematically showing a structure of alight emitting device according to another example embodiment;

FIG. 13 is a perspective view schematically showing an example structureof a reflective layer illustrated in FIG. 12 ;

FIG. 14 is a plan view schematically showing an example structure of thereflective layer illustrated in FIG. 12 ;

FIG. 15A schematically shows light of a short wavelength flowing into arecess formed in a reflective layer;

FIG. 15B schematically shows light of a long wavelength blocked in thereflective layer in which the recess is formed;

FIG. 16 schematically shows light resonating in a light emitting deviceaccording to the example embodiment;

FIG. 17 is a plan view schematically showing another example structureof the reflective layer shown in FIG. 12 ;

FIG. 18 is a perspective view schematically showing another examplestructure of the reflective layer shown in FIG. 12 ;

FIG. 19 is a cross-sectional view schematically showing a structure of adisplay apparatus according to an example embodiment;

FIG. 20 is a cross-sectional view schematically showing a structure of adisplay apparatus according to another embodiment;

FIG. 21 is a cross-sectional view schematically showing a structure of adisplay apparatus according to another example embodiment;

FIG. 22 is a cross-sectional view schematically showing a structure of adisplay apparatus according to another example embodiment; and

FIG. 23 is a cross-sectional view schematically showing a structure of adisplay apparatus according to another example embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to example embodiments of which areillustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the exampleembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theexample embodiments are merely described below, by referring to thefigures, to explain aspects. As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.Expressions such as “at least one of,” when preceding a list ofelements, modify the entire list of elements and do not modify theindividual elements of the list. For example, the expression, “at leastone of a, b, and c,” should be understood as including only a, only b,only c, both a and b, both a and c, both b and c, or all of a, b, and c.

Hereinafter, with reference to the accompanying drawings, a lightemitting device and a display apparatus including the light emittingdevice will be described in detail. Like reference numerals refer tolike elements throughout, and in the drawings, sizes of elements may beexaggerated for clarity and convenience of explanation. The exampleembodiments described below are merely exemplary, and variousmodifications may be possible from the example embodiments.

In a layer structure described below, an expression “above” or “on” mayinclude not only “immediately on in a contact manner” but also “on in anon-contact manner”. An expression used in the singular encompasses theexpression of the plural, unless it has a clearly different meaning inthe context. It will be further understood that the terms “comprises”and/or “comprising” used herein specify the presence of stated featuresor elements, but do not preclude the presence or addition of one or moreother features or elements.

The use of “the” and other demonstratives similar thereto may correspondto both a singular form and a plural form. Unless the order ofoperations of a method according to the present disclosure is explicitlymentioned or described otherwise, the operations may be performed in aproper order. The present disclosure is not limited to the order theoperations are mentioned.

The term used in the example embodiments such as “unit” or “module”indicates a unit for processing at least one function or operation, andmay be implemented in hardware or software, or in a combination ofhardware and software.

The connecting lines, or connectors shown in the various figurespresented are intended to represent functional relationships and/orphysical or logical couplings between the various elements. It should benoted that many alternative or additional functional relationships,physical connections or logical connections may be present in apractical device.

The use of any and all examples, or language provided herein, isintended merely to better illuminate the disclosure and does not pose alimitation on the scope of the disclosure unless otherwise claimed.

FIG. 1 is a cross-sectional view schematically showing a structure of alight emitting device 100 according to an example embodiment. Referringto FIG. 1 , the light emitting device 100 according to an exampleembodiment may include a reflective layer 110 having a phase modulationsurface, a transparent planarization layer 120 disposed on thereflective layer 110, a first electrode 131 disposed on theplanarization layer 120, an organic emission layer 140 disposed on thefirst electrode 131, and a second electrode 132 disposed on the organicemission layer 140. The light emitting device 100 may further include atransparent passivation layer 150 disposed on the second electrode 132to protect the second electrode 132.

The light emitting device 100 may be an organic light emitting diode(OLED). For example, FIG. 2 is a cross-sectional view showing an examplestructure of the organic emission layer 140 illustrated in FIG. 1 inmore detail. Referring to FIG. 2 , the organic emission layer 140 mayinclude a hole injection layer 142 disposed on the planarization layer120, an organic emission material layer 141 disposed on the holeinjection layer 142, and an electron injection layer 143 disposed on theorganic emission material layer 141. In this structure, holes providedthrough the hole injection layer 142 and electrons provided through theelectron injection layer 143 may be combined in the organic emissionmaterial layer 141 to generate light. A wavelength of the generatedlight may be determined according to an energy band gap of a lightemitting material of the organic emission material layer 141.

In addition, the organic emission layer 140 may further include a holetransfer layer 144 disposed between the hole injection layer 142 and theorganic emission material layer 141 in order to further facilitate thetransport of holes. In addition, the organic emission layer 140 mayfurther include an electron transfer layer 145 disposed between theelectron injection layer 143 and the organic emission material layer 141in order to further facilitate the transport of electrons. In addition,the organic emission layer 140 may include various additional layers asnecessary. For example, the organic emission layer 140 may furtherinclude an electron block layer between the hole transfer layer 144 andthe organic emission material layer 141, and may also further include ahole block layer between the organic emission material layer 141 and theelectron transfer layer 145.

The organic emission material layer 141 may be configured to emitvisible light. For example, the organic emission material layer 141 maybe configured to emit light in a wavelength band among a wavelength bandof red light, a wavelength band of green light, and a wavelength band ofblue light. However, embodiments are not limited thereto. For example,the organic emission material layer 141 may be configured to emit whitevisible light including all of red light, green light, and blue light.

For example, FIG. 3 is a cross-sectional view showing another examplestructure of the organic emission layer 140 illustrated in FIG. 1 inmore detail. Referring to FIG. 3 , the organic emission material layer141 may include a first organic emission material layer 141 a that emitsred light, a second organic emission material layer 141 b that emitsgreen light, and a third organic emission material layer 141 c thatemits blue light. Further, an exciton blocking layer 146 may be disposedbetween the first organic emission material layer 141 a and the secondorganic emission material layer 141 b and between the second organicemission material layer 141 b and the third organic emission materiallayer 141 c. Then, the organic emission layer 140 may emit white light.However, the structure of the organic emission layer 140 that emitswhite light is not limited thereto. For example, the organic emissionlayer 140 may include two organic emission material layers incomplementary relation to each other.

The first electrode 131 disposed on the lower surface of the organicemission layer 140 may serve as an anode that provides holes. The secondelectrode 132 disposed on the upper surface of the organic emissionlayer 140 may serve as a cathode that provides electrons. To this end,the first electrode 131 may include a material having a relatively highwork function, and the second electrode 132 may include a materialhaving a relatively low work function.

In addition, the first electrode 131 may be a transparent electrodehaving a property of transmitting light, for example, visible light. Forexample, the first electrode 131 may include transparent conductiveoxide, such as indium tin oxide (ITO), indium zinc oxide (IZO), oraluminum zinc oxide (AZO).

The second electrode 132 may be a semi-transmissive electrode thatreflects a portion of light and transmits the remaining portion oflight. To this end, the second electrode 132 may include a very thinreflective metal. For example, the second electrode 132 may be a mixedlayer of silver (Ag) and magnesium (Mg) or a mixed layer of aluminum(Al) and lithium (Li). The entire thickness of the second electrode 132may be about 10 nm to about 20 nm. Because the thickness of the secondelectrode 132 is very thin, a portion of light may pass through thereflective metal.

The reflective layer 110 may be configured to reflect light generatedfrom the organic emission layer 140 and transmitted through the firstelectrode 131. To this end, the reflective layer 110 may include silver(Ag), gold (Au), aluminum (Al), or an alloy including silver (Ag), gold(Au), and aluminum (Al). However, the reflective layer 110 is notlimited thereto, and may include other reflective materials.

The reflective layer 110 may serves to configure a micro cavity Ltogether with the second electrode 132. For example, the micro cavity Lmay be formed between the reflective layer 110 and the second electrode132 of the light emitting device 100. For example, light generated fromthe organic emission layer 140 may reciprocate and resonate between thereflective layer 110 and the second electrode 132, and then lightcorresponding to the resonance wavelength of the micro cavity L may beemitted to the outside through the second electrode 132.

The resonance wavelength of the micro cavity L formed between thereflective layer 110 and the second electrode 132 may be determined bythe optical length of the micro cavity L. For example, when theresonance wavelength of the micro cavity L is A, the optical length ofthe micro cavity L may be nλ/2, where n is a natural number. The opticallength of the micro cavity L may be determined as the sum of the opticalthickness of layers forming the micro cavity L between the reflectivelayer 110 and the second electrode 132, a phase delay by the secondelectrode 132, and a phase shift, for example, a phase delay by thereflective layer 110. Here, the optical thickness of the layers formingthe micro cavity L between the reflective layer 110 and the secondelectrode 132 is not a simple physical thickness, but is the thicknessconsidering the refractive index of materials of the layers forming themicro cavity L. For example, the optical thickness of the layers formingthe micro cavity L may be the sum of the optical thickness of theplanarization layer 120, the optical thickness of the first electrode131, and the optical thickness of the organic emission layer 140.

According to the example embodiment, the optical length of or theresonance wavelength of the micro cavity L may be adjusted by adjustingonly the phase shift by the reflective layer 110 while fixing theoptical thickness of the layers forming the micro cavity L and the phasedelay by the second electrode 132. In order to control the phase shiftby the reflective layer 110, a phase modulation surface may be formed onthe reflective surface of the reflective layer 110 in contact with theplanarization layer 120. The phase modulation surface may include verysmall patterns in the nanoscale. For example, the phase modulationsurface of the reflective layer 110 may have a meta structure in whichnano patterns having a size smaller than the wavelength of visible lightare periodically disposed.

Referring back to FIG. 1 , the reflective layer 110 may include a base111 and the phase modulation surface formed on an upper surface 114 ofthe base 111. The phase modulation surface of the reflective layer 110may include a plurality of protrusions 112 periodically formed on theupper surface 114 of the base 111. The plurality of protrusions 112 mayhave a post shape protruding from the upper surface 114 of the base 111.For example, the plurality of protrusions 112 may have a cylindricalshape. The plurality of protrusions 112 may be integrally formed withthe base 111. The reflective layer 110 may be disposed such that theplurality of protrusions 112 is in contact with the planarization layer120.

When each of the protrusions 112 is, for example, a cylinder, theoptical characteristics of the phase modulation surface, for example,the phase delay of reflected light may be determined by a diameter W ofeach of the protrusions 112, a height H each of the protrusions 112 anda pitch or period P of the plurality of protrusions 112. When each ofthe protrusions 112 is a polygonal column, the optical characteristicsof the phase modulation surface may be determined by a maximum width Wof each of the protrusions 112, the height H of each of the protrusions112, and the pitch or the period P of the plurality of protrusions 112.

The diameter W, the height H, and the period P of the protrusions 112may be constant with respect to the entire region of the phasemodulation surface. For example, the diameter W of the protrusion 112may be from about 30 nm to about 250 nm, the height H of the protrusion112 may be from about 0 nm to about 150 nm, and the period P of theplurality of protrusions 112 may be from about 100 nm to about 300 nm.

When the size of each of the protrusions 112 of the phase modulationsurface is smaller than the resonance wavelength as described above, aplurality of nano-light resonance structures may be formed whileincident light resonates in the periphery of the protrusions 112. Inparticular, in the incident light, an electric field component may notpenetrate into a space between the protrusions 112, and only a magneticfield component may resonate in the periphery of the protrusions 112.Accordingly, the plurality of nano-light resonant structures formed inthe space between the protrusions 112 may be a cylinder type magneticresonator in which the magnetic field component of the incident lightresonates in the periphery of the protrusions 112. As a result, a phaseshift greater than a simple phase shift due to an effective opticaldistance (H×n) determined by the product of the height H of theprotrusions 112 and a refractive index n of the protrusions 112 mayoccur on the phase modulation surface of the reflective layer 110.

Accordingly, the resonance wavelength of the micro cavity L may bedetermined by the diameter W of each of the protrusions 112 of the phasemodulation surface, the height H of each of the protrusions 112 and theperiod P of the plurality of protrusions 112. For example, when theresonance wavelength of the micro cavity L is A, the diameter W of eachof the protrusions 112 of the phase modulation surface, the height H ofeach of the protrusions 112 and the period P of the plurality ofprotrusions 112 of the phase modulation surface may be selected suchthat the optical length of the micro cavity L satisfies nλ/2, where n isa natural number. Then, the resonance wavelength of the micro cavity Lin the light emitting device 100 may more easily match with the emittingwavelength or emitting color of the light emitting device 100. Forexample, when the light emitting device 100 is a red light emittingdevice, the diameter W of each of the protrusions 112 of the phasemodulation surface, the height H of each of the protrusions 112 and theperiod P of the plurality of protrusions 112 of the phase modulationsurface may be selected such that the resonance wavelength of the microcavity L corresponds to a red wavelength band. As described above, itmay be possible to determine the emitting wavelength of the lightemitting device 100 only by the structure of the phase modulationsurface of the reflective layer 110.

In order to prevent the micro cavity L from having a polarizationdependency, the plurality of protrusions 112 may be regularly andperiodically arranged to have a 4-fold symmetry characteristic. When themicro cavity L has the polarization dependency, only light of a specificpolarization component may resonate, which may deteriorate the lightemitting efficiency of the light emitting device 100. For example, FIG.4 is a perspective view schematically showing an example structure ofthe reflective layer 110 illustrated in FIG. 1 , and FIG. 5 is aperspective view schematically showing another example structure of thereflective layer 110 illustrated in FIG. 1 . Referring to FIG. 4 , theplurality of protrusions 112 having a cylindrical shape on the uppersurface 114 of the base 111 may be regularly arranged two-dimensionally.In addition, referring to FIG. 5 , the plurality of protrusions 112having a square column shape may be regularly arranged two-dimensionallyon the upper surface 114 of the base 111. In FIGS. 4 and 5 , althoughthe protrusion 112 has the cylindrical shape and the square columnshape, the shape of the protrusion 112 is not necessarily limitedthereto. For example, the protrusion 112 may have an elliptical columnor a polygonal column shape of a pentagonal shape or more.

In addition, in FIGS. 4 and 5 , the plurality of protrusions 112 isarranged in a regular two-dimensional array pattern. In this case,intervals between the two adjacent protrusions 112 in the entire regionof a phase modulation surface may be constant. However, if the pluralityof protrusions 112 has a 4-fold symmetry characteristic, the pluralityof protrusions 112 may be arranged in any other type of array. Forexample, the plurality of protrusions 112 may be arranged irregularly.In this case, the micro cavity L may not have a polarization dependency.Meanwhile, in another example embodiment, the arrangement of theplurality of protrusions 112 may be designed differently from the 4-foldsymmetry such that the light emitting device 100 intentionally emitsonly light of a specific polarization component. For example, theplurality of protrusions 112 may be arranged in a one-dimensional arraypattern.

The planarization layer 120 may be disposed on the reflective layer 110having the phase modulation surface including the plurality ofprotrusions 112 to provide a flat surface. The lower surface of theplanarization layer 120 may have a shape complementary to the phasemodulation surface of the reflective layer 110, and the upper surfacethereof has a flat shape. Therefore, the first electrode 131 disposed onthe upper surface of the planarization layer 120 may have a flat lowersurface. Then, the first electrode 131 may apply a uniform electricfield to the organic emission layer 140. The planarization layer 120 mayinclude a material transparent to visible light. In addition, theplanarization layer 120 may include an insulating material to preventcurrent from flowing from the first electrode 131 to the reflectivelayer 110. For example, the planarization layer 120 may include metaloxide such as silicon dioxide (SiO₂), silicon nitride (SiNx), aluminumoxide (Al₂O₃), or hafnium dioxide (HfO₂), metal nitride, or atransparent polymer compound.

Meanwhile, when considering the physical thickness of the organicemission layer 140, the optical length of the micro cavity L may beselected to mainly use a second resonance. In other words, the opticallength of the micro cavity L may be selected to be the same as theemitting wavelength A of the light emitting device 100, where n=2 innλ/2. In this case, a portion of light having a wavelength shorter thanthe emitting wavelength of the light emitting device 100 may generate athird resonance, where n=3, and may be emitted from the light emittingdevice 100. For example, when the light emitting device 100 isconfigured to emit red light, the optical length of the micro cavity Lmay be selected as 630 nm. In this case, part of light having awavelength of 420 nm may generate the third resonance and may be emittedfrom the light emitting device 100. Then, since blue light is emittedfrom the light emitting device 100 together with red light, the colorpurity of light emitted from the light emitting device 100 may bereduced.

According to the example embodiment, in order to suppress the lighthaving the wavelength shorter than the emitting wavelength of the lightemitting device 100 from being emitted from the light emitting device100, the planarization layer 120 may include a light absorber 121 thatabsorbs light in a wavelength band shorter than the emitting wavelengthof the light emitting device 100. The light absorber 121 may beselected, for example, to absorb light in a wavelength band that causesthe third resonance within the micro cavity L of the light emittingdevice 100. Then, the light in the wavelength band causing the secondresonance in the micro cavity L may not be absorbed by the lightabsorber 121 but may be emitted from the light emitting device 100.Meanwhile, the light in the wavelength band causing the third resonancein the micro cavity L may be absorbed by the light absorber 121 in theplanarization layer 120 in a process of repeatedly passing through theplanarization layer 120.

In FIG. 1 , a plurality of light absorbers 121 is uniformly dispersedinside the planarization layer 120. In the planarization layer 120, onlythe material of the light absorber 121 may be mixed and dispersed alone,but embodiments are not limited thereto. For example, the material ofthe light absorber 121 and an organic binder may be mixed and dissolvedin an organic solvent, and then the organic solvent may be applied onthe reflective layer 110 and cured by light or heat, and thus theplanarization layer 120 may be formed.

For example, FIG. 6 is a graph showing an example of the absorptioncharacteristics of the planarization layer 120 including the lightabsorber 121. In FIG. 6 , a material that absorbs blue light is used asthe light absorber 121, and a change in the absorption characteristicsof the planarization layer 120 is measured while changing theconcentration of the material of the light absorber 121 dissolved in anorganic solvent. In the graph of FIG. 6 , the concentration representsthe concentration of the material of the light absorber 121 beforecuring the organic solvent, and an absorbance is measured after curingthe organic solvent to form the planarization layer 120. Referring tothe graph of FIG. 6 , it may be seen that the planarization layer 120has an absorption peak near a wavelength of about 450 nm and theabsorbance increases as the material of the light absorber 121increases.

FIG. 7 is a cross-sectional view showing the structure of a lightemitting device 10 according to a first related example. Referring toFIG. 7 , the light emitting device 10 according to the first relatedexample may include a reflective layer 11, a planarization layer 12, afirst electrode 13, an organic emission layer 14, a second electrode 15and a passivation layer 16. Compared to the light emitting device 100according to the example embodiment, the light emitting device 10 isdifferent in that the reflective layer 11 of the light emitting device10 does not have a phase modulation surface and the planarization layer12 does not include a light absorber.

In addition, FIG. 8 is a cross-sectional view showing the structure of alight emitting device 20 according to a second related example.Referring to FIG. 8 , the light emitting device 20 according to thesecond related example may include a reflective layer 21 having a phasemodulation surface 21 a, a planarization layer 22, a first electrode 23,an organic emission layer 24, a second electrode 25 and a passivationlayer 26. Compared with the light emitting device 100 according to theexample embodiment, the light emitting device 20 is different in thatthe planarization layer 22 of the light emitting device 20 does notinclude a light absorber.

In addition, FIG. 9 is a cross-sectional view showing the structure of alight emitting device 30 according to a third related example. Referringto FIG. 9 , the light emitting device 30 according to the third relatedexample may include a reflective layer 31, a planarization layer 32including a light absorber 32 a, a first electrode 33, an organicemission layer 34, a second electrode 35 and a passivation layer 36.Compared to the light emitting device 100 according to the exampleembodiment, the light emitting device 30 is different in that thereflective layer 31 of the light emitting device 30 does not have aphase modulation surface.

FIG. 10 is a graph showing comparisons of spectrums of light emittedfrom the light emitting devices 10, 20, 30, and 100 according to thefirst to third related examples and the example embodiment. All of thelight emitting devices 10, 20, 30, and 100 according to the first tothird related examples and the example embodiment select optical lengthsof micro cavities such that a second resonance occurs in a wavelengthband of red light. The graph of FIG. 10 illustrates that the intensityof blue light emitted from the light emitting device 10 according to thefirst related example is the greatest. In addition, the intensity ofblue light emitted from the light emitting devices 20 and 30 accordingto the second and third related examples are similar to each other. Inthe light emitting device 100 according to the example embodiment, theemission of blue light is greatly reduced.

In addition, FIG. 11 shows comparisons of color coordinates of lightemitted from the light emitting devices 10, 20, 30, and 100 according tothe first to third related examples and the example embodiment. Thecolor coordinates shown in FIG. 11 are CIE 1934 color coordinates. FIG.11 illustrates that light emitted from the light emitting device 100according to the example embodiment is closest to pure red light. Then,the color purity of the emitted light deteriorates as the color of theemitted light is gradually closer to blue light in the order of thethird related example, the second related example, and the first relatedexample.

As described above, according to the example embodiment, the lightemitting device 100 including a micro cavity may more easily match aresonance wavelength of the micro-cavity to the emitting wavelength ofthe light emitting device 100 by appropriately configuring a phasemodulation surface. In addition, because the planarization layer 120disposed on the phase modulation surface includes a light absorber thatabsorbs light that is not a target light emitting wavelength component,for example, light of another wavelength component that causes a thirdresonance in the micro cavity, the light emitting device 100 may emitonly light of the target emitting wavelength component and suppresslight of the remaining wavelength components. Therefore, the lightemitting device 100 may achieve higher color purity.

FIG. 12 is a cross-sectional view schematically showing a structure of alight emitting device 200 according to another example embodiment.Referring to FIG. 12, the light emitting device 200 according to anotherexample embodiment may include a reflective layer 210 including a phasemodulation surface, a planarization layer 220 disposed on the reflectivelayer 210 and including a light absorber 221, a first electrode 231disposed on the planarization layer 220, an organic emission layer 240disposed on the first electrode 231, and a second electrode 232 disposedon the organic emission layer 240. In addition, the light emittingdevice 200 may further include a transparent passivation layer 250disposed on the second electrode 232. Compared with the light emittingdevice 100 shown in FIG. 1 , the structure of the phase modulationsurface formed on the reflective layer 210 of the light emitting device200 shown in FIG. 12 is different from the structure of a phasemodulation surface of the light emitting device 100 shown in FIG. 1 .The remaining configuration of the light emitting device 200 illustratedin FIG. 12 is the same as that of the light emitting device 100illustrated in FIG. 1 , and thus descriptions thereof will be omitted.

FIG. 13 is a perspective view schematically showing an example structureof the reflective layer 210 illustrated in FIG. 12 , and FIG. 14 is aplan view schematically showing an example structure of the reflectivelayer 210 illustrated in FIG. 12 . Referring to FIGS. 12 to 14 , thephase modulation surface may include a plurality of protrusions 212 anda plurality of recesses 213 periodically disposed on an upper surface214 of a base 211 facing the first electrode 231. The reflective layer210 may be disposed such that the plurality of protrusions 212 and theplurality of recesses 213 are in contact with the planarization layer220.

Each of the protrusions 212 protruding from the upper surface 214 of thebase 211 and each of the recesses 213 recessed from the upper surface214 of the base 211 may have dimensions smaller than the wavelength ofvisible light. As shown in FIGS. 13 and 14 , the protrusions 212 and therecesses 213 may be formed to be spaced apart, and an area occupied bythe upper surface 214 may be greater than an area occupied by theplurality of protrusions 212 or the plurality of recesses 213. Inaddition, the area occupied by each of the protrusions 212 may begreater than or equal to the area occupied by each of the recesses 213.

The plurality of protrusions 212 may be periodically arranged with apredetermined pitch P1 on the upper surface 214 of the base 211. FIG. 14shows an example of the protrusions 212 periodically arranged in theshape of a square array. However, this is merely an example, and inaddition, the plurality of protrusions 212 may be arranged in an arrayof various other shapes such as a regular triangle, a regular hexagon,etc. Each of the protrusions 212 may have, for example, a diameter W1 ofapproximately 300 nm or less. However, each of the protrusions 212 isnot necessarily limited thereto. For example, each of the protrusions212 may have the diameter W1 of approximately 30 nm to 250 nm. Further,each of the protrusions 212 may have, for example, a height H1 ofapproximately 100 nm or less. However, these numerical values are onlyexamples.

As described above, the plurality of protrusions 212 may serve to adjustthe optical length of the micro cavity L to resonate light correspondingto the emitting wavelength of the light emitting device 200. Forexample, when the resonance wavelength of the micro cavity L is A, thediameter W1 and the height H1 of each of the protrusions 212 of thephase modulation surface and the pitch P1 of the protrusions 212 may beselected such that the optical length of the micro cavity L satisfiesnλ/2, where n is a natural number.

The plurality of recesses 213 may be formed at a predetermined depth H2on the upper surface 214 of the base 211. The plurality of recesses 213may be periodically two-dimensionally arranged with a predeterminedpitch P2 between the plurality of protrusions 212. FIGS. 13 and 14 showexamples of each of the recesses 213 disposed between the two adjacentprotrusions 212. Each of the recesses 213 may be formed in a cylindricalshape. Each of the recesses 213 may have, for example, a diameter W2 ofapproximately 250 nm or less. More specifically, for example, each ofthe recesses 213 may have a diameter W2 of approximately 80 nm to 250nm, but is not limited thereto. Further, each of the recesses 213 mayhave, for example, a depth H2 of approximately 100 nm or less but thisis merely an example. In addition, a difference between the diameter W1of each of the protrusions 212 and the diameter W2 of each of therecesses 213 may be, for example, approximately 100 nm or less, but isnot limited thereto.

The plurality of the recesses 213 may serve to absorb light of awavelength of which resonance is not desired within the micro cavity L.FIG. 15A schematically shows light of a short wavelength flowing intothe recess 213 formed in the reflective layer 210, and FIG. 15Bschematically shows light of a long wavelength blocked in the reflectivelayer 210 in which the recess 213 is formed. As shown in FIG. 15A, thelight of the short wavelength flows into and is absorbed in thenano-sized recess 213 formed in the upper surface 214 of the base 211,whereas, as shown in FIG. 15B, the light of the long wavelength does notflow into the recess 213 and is reflected from the upper surface 214 ofthe base 211.

The wavelength of the light absorbed into the recess 213 formed in thereflective layer 210 may vary according to the size of the recess 213.For example, when the protrusions 212 are not considered, the recess 213having a diameter of approximately 190 nm formed on the surface of theflat reflective layer 210 including silver (Ag) may absorb blue light ofa wavelength of 450 nm, and the recess 213 having a diameter ofapproximately 244 nm may absorb green light of a wavelength of 550 nm.

As described above, in the light emitting device 200 configured to emitred light, when the optical length of the micro cavity L is selected as630 nm, a portion of light of a wavelength of 420 nm may cause a thirdresonance to be emitted from the light emitting device 200. Then,because blue light is emitted from the light emitting device 200together with red light, the color purity of light emitted from thelight emitting device 200 may be reduced. In the example embodiment,light of a wavelength of which resonance is not desired may be absorbedby the light absorber 221 in the planarization layer 220. In addition,the light of the wavelength of which resonance is not desired may beadditionally absorbed by the recess 213 by forming the plurality ofnano-sized recesses 213 along with the plurality of protrusions 212 onthe phase modulation surface of the reflective layer 210. Therefore, thecolor purity of the light emitting device 200 may be further improved.

FIG. 16 schematically shows light resonating in the light emittingdevice 200 according to the example embodiment. In FIG. 16 , a red lightemitting device is illustrated as the light emitting device 200 as anexample, and for convenience, only the reflective layer 210 and thesecond electrode 232 constituting the micro cavity L are illustrated.Referring to FIG. 16 , in the micro cavity L, a red light R may not flowinto the recess 213 formed in the surface of the reflective layer 210but may be reflected from the surface of the reflective layer 210.However, it may be seen that a blue light B having a wavelength shorterthan the red light R flows into and is absorbed in the recess 213 formedin the surface of the reflective layer 210. As described above, each ofthe recesses 213 may have, for example, a diameter of approximately 250nm or less. Accordingly, in the micro cavity L, only the red light R mayresonate and be emitted outside the light emitting device 200.

According to an example embodiment, the light emitting device 200 may bea green light emitting device. In general, in a case where the surfaceof a reflective layer has a flat structure, when a second resonance of agreen light occurs in a micro cavity, a third resonance of anultraviolet light occurs, which does not affect a display apparatus in avisible light region. However, when the reflective layer 210 having thephase modulation surface is used, there is a possibility that a thirdresonance of the blue light B occurs in the micro cavity L due to thephase modulation. In addition, because the optical length variesaccording to the refractive index and thickness of the planarizationlayer 220, the resonance wavelength may change. Accordingly, blue lightB of an undesired short wavelength in the green light emitting devicemay be emitted. Therefore, even when the light emitting device 200 isthe green light emitting device, the undesired emission of the bluelight B may be further suppressed by forming the plurality of recesses213 in the surface of the reflective layer 210 and dispersing the lightabsorber 221 in the planarization layer 220.

As described above, by forming the plurality of recesses 213 in thephase modulation surface of the reflective layer 210 and dispersing thelight absorber 221 in the planarization layer 220, light having a longwavelength of which resonance is desired, for example, red light orgreen light, may resonate and be emitted, and light of a shortwavelength, for example, blue light of which resonance is not desiredmay be absorbed, and thus color purity may be further improved.

FIG. 17 is a plan view schematically showing another example structureof the reflective layer 210 shown in FIG. 12 . In the example embodimentshown in FIGS. 13 and 14 , the protrusions 212 are periodically arrangedin a square array, and each of the recesses 213 may be formed betweenthe two adjacent protrusions 212. In the reflective layer 210 shown inFIG. 17 , the protrusions 212 protruding from the upper surface 214 ofthe base 211 may be periodically arranged in the square array, and therecesses 213 may be arranged between the two protrusions 212 arrangedadjacent to each other in a diagonal direction on the upper surface 214of the base 211 at a predetermined depth. In other words, each of therecesses 213 may be disposed in the center of a unit array of a squareshape including the four adjacent protrusions 212. However, this ismerely an example, and the protrusions 212 and the recesses 213 may bearranged in various other shapes.

In addition, FIG. 18 is a perspective view schematically showing anotherexample structure of the reflective layer 210 shown in FIG. 12 . In theexample embodiment shown in FIGS. 13 and 14 , the protrusions 212 have acylindrical shape and the recesses 213 are formed in a cylindricalshape. In the metal reflective layer 210 shown in FIG. 18 , theprotrusions 212 have a square column shape. In this case, the maximumwidth of the protrusion 212 may correspond to the diameter. In addition,the recesses 213 may be formed in the cylindrical shape between the twoadjacent protrusions 212. However, this is merely an example, and eachof the protrusions 212 may have a variety of other polyprism shapes,such as a triangular column or a pentagonal column. In addition, each ofthe recesses 213 may also be formed in various other shape.

The above-described light emitting devices 100 and 200 may be applied toa plurality of pixels of a display apparatus. FIG. 19 is across-sectional view schematically showing a structure of a displayapparatus 1000 according to an example embodiment. Referring to FIG. 19, the display apparatus 1000 may include a plurality of pixels that emitlight of different colors. Here, the plurality of pixels may include ared pixel 1100, a green pixel 1200, and a blue pixel 1300 disposedadjacent to each other on the same plane of a substrate. For example,only one unit pixel including the red pixel 1100, the green pixel 1200,and the blue pixel is illustrated for convenience.

The red pixel 1100 may have the same structure as the light emittingdevice 100 illustrated in FIG. 1 . The red pixel 1100 may include afirst reflective layer 1110 including a first phase modulation surface,a first planarization layer 1120 disposed on the first reflective layer1110, a first electrode 1131 disposed on the first planarization layer1120, an organic emission layer 1140 disposed on the first electrode1131, and a second electrode 1132 disposed on the organic emission layer1140. The red pixel 1100 may further include a transparent passivationlayer 1150 disposed on the second electrode 1132. The first reflectivelayer 1110 may include a plurality of first protrusions 1112 formed toprotrude on an upper surface 1114 of a base 1111. The first reflectivelayer 1110 may form a first micro cavity that resonates the red light Rtogether with the second electrode 1132. Also, the first planarizationlayer 1120 may include a light absorber 1121 that absorbs blue light B.

The green pixel 1200 may have the same structure as the light emittingdevice 100 shown in FIG. 1 . The green pixel 1200 may include a secondreflective layer 1210 including a second phase modulation surface, asecond planarization layer 1220 disposed on the second reflective layer1210, the first electrode 1131 disposed on the second planarizationlayer 1220, the organic emission layer 1140 disposed on the firstelectrode 1131, the second electrode 1132 disposed on the organicemission layer 1140, and the passivation layer 1150 disposed on thesecond electrode 1132. The second reflective layer 1210 may include aplurality of second protrusions 1212 formed to protrude over an uppersurface 1214 of a base 1211. The second reflective layer 1210 may form asecond micro cavity that resonates the green light G together with thesecond electrode 1132. In the case of the green pixel 1200, the secondplanarization layer 1220 may not include a light absorber.

In addition, the blue pixel 1300 may include a third reflective layer1310, a third planarization layer 1320 disposed on the third reflectivelayer 1310, a first electrode 1131 disposed on the third planarizationlayer 1320, the organic emission layer 1140 disposed on the firstelectrode 1131, the second electrode 1132 disposed on the organicemission layer 1140, and the passivation layer 1150 disposed on thesecond electrode 1132. The upper surface of the third reflective layer1310 in the blue pixel 1300 may include a flat reflective surface. Also,the third planarization layer 1320 may not include a light absorber.

The third reflective layer 1310 may form a third micro cavity thatresonates blue light B together with the second electrode 1132. Thethird micro cavity may have a resonance wavelength of the blue light Bby adjusting structural and optical characteristics of the layersdisposed between the third reflective layer 1310 and the secondelectrode 1132. Here, the upper surface of the third reflective layer1310 may be formed at the same height as the upper surfaces of the firstprotrusions 1112 of the first phase modulation surface and the secondprotrusions 1212 of the second phase modulation surface. The thirdreflective layer 1310 may have a third phase modulation surface having aresonance wavelength of the blue light B. In this case, the third phasemodulation surface may include a plurality of protrusions that protrudeat a predetermined height on the upper surface of the third reflectivelayer 1310.

In the display apparatus 1000 according to the example embodiment havingthe above structure, the first reflective layer 1110, the secondreflective layer 1210, and the third reflective layer 1310 of the redpixel 1100, the green pixel 1200, and the blue pixel 1300 adjacent toeach other may continuously extend. Also, the first planarization layer1120, the second planarization layer 1220, and the third planarizationlayer 1320 may also continuously extend to each other. Also, the firstelectrodes 1131 of the red pixel 1100, the green pixel 1200, and theblue pixel 1300 may integrally extend. For example, the first electrode1131 may be a common electrode. For independent driving of the red pixel1100, the green pixel 1200, and the blue pixel disposed adjacent to eachother, the organic emission layers 1140 and the second electrodes 1132of the red pixel 1100, the green pixel 1200, and the blue pixel 1300 maybe separated from each other. For example, the second electrode 1132 maybe a pixel electrode. In addition, the red pixel 1100, the green pixel1200, and the blue pixel 1300 may include the same organic emissionlayer 1140. In this case, the organic emission layer 1140 may beconfigured to emit white light.

In the red pixel 1100, in the white light generated in the organicemission layer 1140, the red light R may reciprocate and resonatebetween the first reflective layer 1110 and the second electrode 1132,and then may be emitted to the outside through the second electrode1132. At this time, in the white light generated in the organic emissionlayer 1140, the blue light B may be absorbed by the light absorber 1121in the first planarization layer 1120, and thus the red light R withimproved color purity may be emitted in the red pixel 1100.

In the green pixel 1200, in the white light generated from the organicemission layer 1140, the green light G may reciprocate and resonatebetween the second reflective layer 1210 and the second electrode 1132and then may be emitted to the outside through the second electrode1132. In addition, in the blue pixel 1300, in the white light generatedin the organic emission layer 1140, the blue light B may reciprocate andresonate between the third reflective layer 1310 and the secondelectrode 1132, and then may be emitted to the outside through thesecond electrode 1132.

According to the example embodiment, the red pixel 1100 and the greenpixel 1200 may respectively include the plurality of first protrusions1112 and the plurality of second protrusions 1212 that have the firstphase modulation surface and the second phase modulation surface havingthe sizes smaller than the wavelength of incident light and periodicallydisposed, and may more easily induce resonance of a desired wavelengthby adjusting the sizes and pitches of the first protrusions 1112 and thesecond protrusions 1212. Accordingly, in order to adjust the opticallength of a micro cavity of each of the red pixel 1100, the green pixel1200, and the blue pixel 1300, the physical thickness of each of the redpixel 1100, the green pixel 1200, and the blue pixel 1300 may not needto be individually adjusted, and only the first phase modulation surfaceof the red pixel 1100 and the second phase modulation surface of thegreen pixel 1200 may be individually configured. Then, the physicalthicknesses of the red pixel 1100, the green pixel 1200, and the bluepixel 1300 may all be the same. In addition, the upper surfaces of thefirst protrusions 1112 and the second protrusions 1212 in the red pixel1100 and the green pixel 1200 may be formed to have the same height asthe upper surfaces of the third reflective layer 1310 in the blue pixel1300. Thus, the display apparatus 1000 may be manufactured more easily.In addition, the light absorber 1121 in the first planarization layer1120 of the red pixel 1100 may absorb the blue light B, and thus thecolor purity of the red light R emitted from the red pixel 1100 may beimproved.

FIG. 20 is a cross-sectional view schematically showing a structure of adisplay apparatus 2000 according to another example embodiment. In thecase of the display apparatus 2000 illustrated in FIG. 20 , the secondplanarization layer 1220 of the green pixel 1200 may further include thelight absorber 1121 that absorbs the blue light B. Then, the colorpurity of the green light G emitted from the green pixel 1200 may beimproved. Here, the light absorber 1121 disposed on the firstplanarization layer 1120 of the red pixel 1200 and the light absorber1121 disposed on the second planarization layer 1220 of the green pixel1200 may include the same material or different materials. For example,the light absorber 1121 disposed on the first planarization layer 1120of the red pixel 1200 may be selected as a material that does not absorbthe red light R, and the light absorber 1121 disposed on the secondplanarization layer 1220 of the green pixel 1200 may be selected as amaterial that does not absorb the green light G.

In addition, FIG. 21 is a cross-sectional view schematically showing astructure of a display apparatus 3000 according to another exampleembodiment. In the display apparatus 3000 illustrated in FIG. 21 , aplanarization layer of all pixels may include the light absorber 1121that absorbs the blue light B. In other words, the light absorbers 1121of the same material that absorbs the blue light B may be dispersed inthe first planarization layer 1120 of the red pixel 1100, the secondplanarization layer 1220 of the green pixel 1200, and the thirdplanarization layer 1320 of the blue pixel 1300. Then, the firstplanarization layer 1120, the second planarization layer 1220, and thethird planarization layer 1320 of the red pixel 1100, the green pixel1200, and the blue pixel 1300 may be formed more simply in a singleprocess.

As illustrated in FIG. 21 , the distance between the upper surface ofthe third reflective layer 1310 and the lower surface of the firstelectrode 1131 may be the shortest in the blue pixel 1300. In the redpixel 1100, the distance between the upper surface 1114 of the base 1111of the first reflective layer 1110 and the lower surface of the firstelectrode 1131 may be the longest. Therefore, in the third planarizationlayer 1320 of the blue pixel 1300, because a path through which the bluelight B passes is the shortest, the loss of the blue light B due to thelight absorber 1121 in the third planarization layer 1320 may berelatively small. In addition, in the first planarization layer 1120 ofthe red pixel 1100, because a path through which the blue light B passesis the longest, the blue light B may be sufficiently absorbed by thelight absorber 1121 in the first planarization layer 1120.

FIG. 22 is a cross-sectional view schematically showing a structure of adisplay apparatus 4000 according to another example embodiment.Referring to FIG. 22 , the first reflective layer 1110 of the red pixel1100 of the display apparatus 4000 may further include a plurality offirst recesses 1113 that absorb the blue light B. The second reflectivelayer 1210 of the green pixel 1200 may include only the secondprotrusion 1212. Accordingly, the first recess 1113 together with thelight absorber 1121 in the red pixel 1100 may absorb the blue light B,and thus the color purity of the red light R emitted from the red pixel1100 may be improved.

In addition, FIG. 23 is a cross-sectional view schematically showing astructure of a display apparatus 5000 according to another exampleembodiment. Referring to FIG. 23 , the first reflective layer 1110 ofthe red pixel 1100 of the display apparatus 5000 may further include theplurality of first recesses 1113 that absorb the blue light B, and thesecond reflective layer 1210 of the green pixel 1200 may further includea plurality of second recesses 1213 that absorb the blue light B.

In FIGS. 22 and 23 , only the red pixel 1100 includes the light absorber1121, but is not limited thereto. For example, as in the exampleembodiment illustrated in FIG. 20 , in the example embodiments of FIGS.22 and 23 , the red pixel 1100 and the green pixel 1200 may include thelight absorber 1121. Also, as in the example embodiment illustrated inFIG. 21 , in the example embodiments of FIGS. 22 and 23 , the red pixel1100, the green pixel 1200, and the blue pixel 1300 may all include thelight absorber 1121.

It should be understood that example embodiments described herein shouldbe considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each exampleembodiment should typically be considered as available for other similarfeatures or aspects in other embodiments.

While example embodiments have been described with reference to thefigures, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope as defined by the following claims.

What is claimed is:
 1. A display apparatus comprising: a first pixel configured to emit light of a first wavelength; and a second pixel configured to emit light of a second wavelength different from the first wavelength, wherein the first pixel comprises: a reflective layer comprising a phase modulation surface; a planarization layer disposed on the reflective layer; a first electrode disposed on the planarization layer; an organic emission layer disposed on the first electrode and configured to emit visible light that comprises the light of the first wavelength and the light of the second wavelength that is shorter than the first wavelength; and a second electrode disposed on the organic emission layer, wherein second pixel comprises: the reflective layer comprising a flat surface; the planarization layer disposed on the reflective layer in the second pixel; the first electrode disposed on the planarization layer in the second pixel; the organic emission layer disposed on the first electrode in the second pixel and configured to emit the visible light that comprises the light of the first wavelength and the light of the second wavelength; and the second electrode disposed on the organic emission layer in the second pixel, wherein the reflective layer in the first pixel and the second electrode in the first pixel form a micro cavity configured to resonate the light of the first wavelength, and wherein the planarization layer in the first pixel comprises a light absorber configured to absorb the light of the second wavelength and the planarization layer in the second pixel does not comprise a light absorber configured to absorb the light of the second wavelength.
 2. The display apparatus of claim 1, wherein the phase modulating surface of the reflective layer in the first pixel comprises a plurality of protrusions that are periodically two-dimensionally formed, and wherein a resonance wavelength of the micro cavity in the first pixel is determined by a width or a diameter of each of the plurality of protrusions, a height of each of the plurality of protrusions, and distances between the plurality of protrusions.
 3. The display apparatus of claim 2, wherein, when the first wavelength is λ, a width or a diameter of each of the plurality of protrusions, a height of each of the plurality of protrusions, and distances between the plurality of protrusions are set such that an optical length of the micro cavity is equal to nλ/2, where n is a natural number.
 4. The display apparatus of claim 2, wherein the phase modulating surface of the reflective layer in the first pixel further comprises a plurality of recesses that are periodically two-dimensionally formed.
 5. The display apparatus of claim 4, wherein the plurality of recesses are configured to absorb the light of the second wavelength.
 6. The display apparatus of claim 4, wherein the plurality of protrusions and the plurality of recesses contact the planarization layer in the first pixel.
 7. The display apparatus of claim 4, wherein a dimension of each of the plurality of protrusions and a dimension of each of the plurality of recesses is less than a wavelength of the visible light.
 8. The display apparatus of claim 1, wherein the reflective layer in the second pixel and the second electrode in the second pixel form a micro cavity configured to resonate the light of the second wavelength.
 9. The display apparatus of claim 1, wherein the reflective layer in the first pixel and the reflective layer in the second pixel extend continuously.
 10. The display apparatus of claim 1, wherein the planarization layer in the first pixel and the planarization layer in the second pixel extend continuously.
 11. The display apparatus of claim 1, wherein a physical thickness of the first pixel and a physical thickness of the second pixel are same.
 12. The display apparatus of claim 1, wherein the visible light is white light, the light of the first wavelength comprises red light or green light, and the light of the second wavelength comprises blue light.
 13. The display apparatus of claim 1, further comprising a third pixel configured to emit light of a third wavelength different from the first wavelength and the second wavelength, wherein the third pixel comprises: the reflective layer comprising the phase modulation surface; the planarization layer disposed on the reflective layer in the third pixel; the first electrode disposed on the planarization layer in the third pixel; the organic emission layer disposed on the first electrode in the third pixel and configured to emit the visible light that comprises the light of the first wavelength, the light of the second wavelength, and the light of the third wavelength; and the second electrode disposed on the organic emission layer in the third pixel, wherein the reflective layer in the third pixel and the second electrode in the third pixel form a micro cavity configured to resonate the light of the third wavelength.
 14. The display apparatus of claim 13, wherein the planarization layer in the third pixel comprises the light absorber configured to absorb the light of the second wavelength that is shorter than the third wavelength.
 15. The display apparatus of claim 15, wherein the light absorber in the first pixel and the light absorber in the third pixel comprise different materials.
 16. The display apparatus of claim 13, wherein the planarization layer in the third pixel does not comprise a light absorber configured to absorb the light of the second wavelength.
 17. The display apparatus of claim 13, wherein a physical thickness of the first pixel, a physical thickness of the second pixel, and a physical thickness of the third pixel are same.
 18. The display apparatus of claim 13, wherein the visible light is white light, the light of the first wavelength comprises red light, the light of the second wavelength comprises blue light, and the light of the third wavelength comprises green light.
 19. The display apparatus of claim 13, wherein the organic emission layer in the first pixel and the organic emission layer in the second pixel are configured to further emit the light of the third wavelength.
 20. The display apparatus of claim 13, wherein the phase modulating surface of the reflective layer in the third pixel comprises a plurality of protrusions that are periodically two-dimensionally formed, and wherein a resonance wavelength of the micro cavity in the third pixel is determined by a width or a diameter of each of the plurality of protrusions, a height of each of the plurality of protrusions, and distances between the plurality of protrusions. 